1. Field of the Invention
This invention relates to metal forming, and particularly to a method for forming a material which has corrugations in two directions.
2. Description of the Prior Art
U.S. Pat. No. 3,376,684, issued to D. W. Cole et al., discloses a double reverse corrugated material and a method for making this material. As described in the Cole patent, the material is an open, truss form or reticulated structural material having two basic and integrally connected elements--strut-like members which extend between upper and lower crest-bent nodals, and cripples which are members extending from a median fold position substantially on the median plane of the material to the crest-bent nodals. The resulting material provides unique structural advantages as use for core material or as fencing material. As described in the Cole patent, this double reverse corrugated material differs from well known conventional corrugated material because alternate corrugations have been reversed so as to halve the pitch span of the resultant structure without alteration of height, depth or overall area.
The aforementioned Cole patent also describes a method of manufacture of a double reverse corrugated material which comprises three basic steps. First, flat metal stock sheet is provided with longitudinally cut, slit, or chemically etched slots. Generally, such slots would be pierced through the sheet by means of a piercing die. The slots are symetrically staggered, offset, or laterally displaced, row from row and column from column. Second, a slotted sheet stock undergoes an initial strike in a conventional sheet metal brake in which the area between the slots is alternately displaced upward and downward to form the corrugations. Third and last, the double reverse corrugated material is formed by restriking the "initial strike" corrugation. The restrike is accomplished by a set of matched dies having flattened portions extending outwardly from a median plane and cup-like cavities extending inwardly therefrom. The initial strike corrugated material is fed into the restrike area by suitable feed mechanisms. While the resulting double reverse corrugating material is extremely valuable, the three step process described in the aforementioned Cole patent is time-consuming and makes the resulting material expensive to produce.
Since the issuance of the aforementioned Cole patent, the method of manufacture of double reverse corrugated material has been simplified somewhat. However, until now, it has not been possible to form the material in a single automatic operation. One problem with forming this material by a single strike has been removing the corrugated material from the forming die. Any attempt to forcibly remove the material during the forming process can result in the material being deformed as it is removed from the die. As a result, it has heretofore been necessary to undertake some preforming step prior to the final strike of the material, or to meticulously strip the material manually from the forming dies after each single strike.